1. Field of the Invention
The invention relates to a method for forming a GexSi1−x buffer layer, particularly to a method for forming a GexSi1−x buffer layer of solar-energy battery on a silicon wafer.
2. Description of the Prior Art
The germanium-based (Ge) as a base substrate of InGaP/InGaAs/GaAs/Ge solar cell has become the main structure of III-V triple-junction solar cell, since the emergence of high-efficiency III-V triple-junction solar cell facing the world. In other words, these solar cells are composed of the gallium arsenide (GaAs) material system. At present, a lot of materials can be matched with the GaAs lattice, such as InGaAsP, InGaAlP, and AlGaAs etc. The growth technology of these materials is very mature, which is used by the industry widely. Due to these materials own the larger energy gap, they are able to be used on the junction with energy gap greater than GaAs. When the energy gap is smaller than GaAs, except germanium, it is very difficult to find other mature materials which can match with the GaAs lattice.
In the conventional GaAs solar cell fabrication process, the Metal Organic Chemical Vapor Deposition (MOCVD) is usually employed to deposit the Ge layer, InGaP layer, InGaAs layer, and the buffer layers sequentially on the germanium substrate by series packing, finally the electrodes and anti-reflect layers are coated on both ends of above-mentioned layers to form the finished product of solar cell. The absorption spectrum distribution and power generation efficiency of solar cell will be influenced by the composed elements of every conjunction layer, the lattice matching of every epitaxial layer, and the quality of crystal-type, in order to fabricate the high-efficiency solar cell that is best the lattice matching and the best energy gap distribution, also, the composed elements of every conjunction layer, the lattice matching of every epitaxial layer, and the quality of crystal-type will often become the key-point of bottleneck and fabrication yield for the technological development of solar cell.
Thus in the conventional technological area of solar energy, the germanium substrate is collected. The III-V semiconductors are grown on the germanium substrate. The total weight is relatively heavy, and the price of germanium substrate is quite higher as well. The maximum size of germanium substrate is only 4 inches, and it is unable to produce larger product. Thus the cost of Ge-based solar cell cannot be reduced for the industrial requirement.
In addition, the conventional method usually use Si1−xGex (x=0˜1) to grow the germanium on the silicon wafer. This method has the shortcomings, such as thicker SiGe buffer layer (up to about 10 μm), higher manufacturing cost and difficult fabrication process integration. And the surface of Ge will be rougher due to the generation of cross hatch pattern.
Thus in order to respond the demand for the related technology of solar cell, it is necessary to develop relevant technologies of solar cell, to save the cost of manpower and time, and to form the high-efficiency solar cell.